How biodiversity loss is like LeBron James and Miami Heat

Ecologists have been saying for decades now that the world is in the midst of a biodiversity crisis. Hundreds of species are vanishing every year, thanks to assaults to the environment that include deforestation, overfishing, toxic pollution and, increasingly, climate change — the lethal icing on an already poisoned cake. Twenty years ago, 150 countries signed the international Convention on Biodiversity to try and hold back the tide of extermination, but without much success: scientists are now saying the planet may be going through its sixth mass extinction in the past 540 million years, and the first caused by humans.

But experts haven’t been so good at explaining exactly why this is such a terrible thing. “Most of the arguments have been based on the idea that biodiversity has some intrinsic value,” said Bradley Cardinale, an ecologist at the University of Michigan, in an interview yesterday. “We like it. It’s pretty. The Pope says we should conserve God’s creation. Maybe we’ll find new medicinal plants in the rainforest.”

In a new paper just published in Nature, however, Cardinale and 17 colleagues have made a much more solid argument. “We’re saying that biodiversity does things that are really important,” he said. “There’s really strong evidence that if we lose biodiversity, it will, among other things, affect food production and fresh water supplies and increase the frequency of pests and diseases that affect crops and animals.”

The paper is what’s known as a meta-analysis: the 18 authors, all of them leaders in the field of ecology, gathered more than a thousand studies published over the past 20 years that looked at biodiversity from a myriad of angles. Then they looked at whether differences in biodiversity affected an ecosystem’s ability to do useful things — the ability of a forest to remove carbon from the atmosphere, for example, or supply wood for construction; the ability of bacteria in a stream to neutralize pollutants; the ability of natural predators and parasites to control agricultural pests.

The answer, it turns out, is yes, to these and many other similar questions. In many cases, it boils down to two primary reasons. The first is that the most diverse ecosystems tend to include what the scientists call “super species.” Say you’re talking about the capacity of a diverse forest to produce wood, or to take carbon from the air, Cardinale said.

“About 50 percent of that effect will come from a single, highly productive species,” he said. The other half comes from a wide variety of other species that occupy different niches, grow at different rates. “It’s like the Miami Heat,” he said. “Half of their productivity comes from LeBron James, but without a strong supporting cast of players, that would not be enough.”

This 50-50 rule is one of six major “consensus statements” all of the scientists were able to agree on, even though some of the 18 disagree with others on narrower details. The others, paraphrased:

The evidence is unequivocal that biodiversity loss makes ecosystems less efficient at producing biomass and at decomposing and recycling biologically essential nutrients.

The evidence is mounting that biodiversity increases the stability of these ecosystem functions

The impact of biodiversity on any single biological process within an ecosystem accelerates as biodiversity loss increases.

Loss of diversity over many trophic levels — that is, levels on the food chain — can be more damaging than the loss of diversity within trophic levels

The effects of biodiversity loss depend on what functions the lost species served in an ecosystem. In other words, some species are more crucial than others.

What the new analysis doesn’t do is put a dollar figure on how the loss of biodiversity impacts us. “We’re not at a point where we can do this realistically,” Cardinale said. “It’ll probably be five or 10 years before we have enough information.”

It’s also unclear at this point how quickly and easily ecosystems can readjust after they go through major species loss. “The term ‘fragile ecosystem’ is much more common in pop environmentalism than in science,” Cardinale said. “Ecosystems can be very robust.” The area around Chernobyl, he noted, is thriving. “It’s a great example of resilience and robustness. But at this point, we don’t know what the norm is.”

One way or another, Cardinale said, “biology will go on. But we don’t know whether it will go in a way that’s good for humanity.”